Linear image sensor

ABSTRACT

In a linear image sensor, a circuit region including a number of photosensitive elements is provided at a center zone of the chip in a longitudinal direction of an elongated semiconductor chip. Two groups of bonding pads are locally concentrated in opposite end zones of the elongated chip, respectively. A plurality of bonding stitches formed on a package for supporting the substrate are divided into two arrays which include substantially the same number of bonding stitches and which are located at both sides of the substrate. Thus, an empty area in the chip can be made as small as possible, and therefore, the chip size can be minimized.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a linear image sensor, and morespecifically to a layout of bonding pads and location of bondingstitches in the linear image sensor.

2. Description of related art

In conventional linear image sensors, an image sensor chip, which isgenerally formed of a semiconductor substrate, has an active area orcircuit region including a number of photosensitive elements arrangedand aligned in a single straight array. In a typical example, the sizeof the circuit region is 300 μm×30,000 μm in a plan view. Namely, thecircuit region is extremely oblong. On the other hand, the requirednumber of bonding pads to be formed on the chip is relatively small.Therefore, if the bonding pads were located and distributed at aperiphery of the circuit region, a substantial invalid or empty areainevitably occur in a peripheral region of the circuit region.

Japanese Patent Application Laid-open No. Hei 2-065278 published on Mar.5, 1990 shows some layouts of various elements within the linear imagesensor chip for the purpose of making the empty area in the chip assmall as possible. In one shown layout, the chip is formed of anelongated semiconductor substrate, and the circuit region including anumber of photosensitive elements is provided at a center zone of thechip in a longitudinal direction of the elongated chip. Bonding pads aredivided into two groups, which are locally arranged at opposite endzones of the elongated chip, respectively. Since the two groups ofbonding pads are concentrated in the opposite end zones of the elongatedchip, the empty area of the periphery of the circuit region on the chipcan be reduced to some degree.

However, in each opposite end zone of the elongated chip, the bondingpads are arranged in two rows, which are separated from each other in atransverse direction perpendicular to the longitudinal direction of theelongated chip. Therefore, the two rows of the bonding pads require asubstantial width, which is considerably larger than the width of thecircuit region, with the result that a substantial empty area remains ateach side of the circuit region along the longitudinal direction of thecircuit region.

On a package substrate for supporting the sensor chip thereon, there areprovided a number of bonding stitches to be connected to the bondingpads of the sensor chip through bonding wires. A minimum pitch of thebonding stitches is considerably larger than a minimum pitch of thebonding pads, and this difference in pitch has restricted the locationof the bonding pads and the bonding stitches, with the result that thereduction of the length and width of the sensor chip is limited. Thismeans that a substantial empty area still remains in the elongated chip.In addition, the difference in pitch has required a long bonding wire,and in extreme cases, makes it difficult to connect between the bondingpads and the bonding stitches by the bonding wires.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide alinear image sensor which has overcome the above mentioned defect of theconventional one.

Another object of the present invention is to provide a linear imagesensor having a minimized empty area on a linear image sensor chip, by anovel layout of bonding pads on the linear image sensor chip and a novellocation of bonding stitches on a package substrate for supporting thelinear image sensor chip.

The above and other objects of the present invention are achieved inaccordance with the present invention by a linear image sensorcomprising:

a linear sensor chip formed of an elongated semiconductor substrate andincluding a circuit region having therein a number of photosensitiveelements and located in a center zone of the substrate in a longitudinaldirection of the substrate, and a pair of bonding pad groups located inopposite end zones of the substrate and at the outside of opposite endsof the circuit region, each of the bonding pad groups including aplurality of bonding pads formed on the substrate;

a package for supporting the substrate thereon, and including aplurality of bonding stitches formed on the package, the bondingstitches being divided into first and second arrays which includesubstantially the same number of bonding stitches and which are locatedin parallel to a longitudinal direction of the substrate so that thefirst array of bonding stitches are arranged at one side of thesubstrate, and the second array of bonding stitches are arranged at theother side of the substrate, the bonding stitches being also dividedinto first and second groups which include substantially the same numberof bonding stitches and which are separated from each other in thelongitudinal direction of the substrate so that the first group ofbonding stitches are positioned in the proximity of one of the end zonesof the substrate, and the second group of bonding stitches arepositioned in the proximity of the other of the end zones of thesubstrate; and

a number of bonding wires each connecting one of the bonding pads to acorresponding one of the bonding stitches without crossing anotherbonding wire.

The above and other objects, features and advantages of the presentinvention will be apparent from the following description of preferredembodiments of the invention with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial diagrammatic plan view of a first embodiment of thelinear image sensor in accordance with the present invention; and

FIG. 2 is a view similar to FIG. 1 but showing a second embodiment ofthe linear image sensor in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a partial diagrammatic plan view ofa first embodiment of the linear image sensor in accordance with thepresent invention.

The shown linear image sensor includes a linear image sensor chip 10formed of an elongated semiconductor substrate 1, a substantial middleportion of which is cut away in the drawing for only simplification ofdrawing. A circuit region 2 having therein a number of photosensitiveelements 12 aligned in a single straight line is located in a centerzone 1A of the substrate 1 in a longitudinal direction of the substrate.A pair of bonding pad groups each including a plurality of bonding pads4 formed on the substrate 1 and arranged in a straight line, are locatedin opposite end zones 1B and 1C of the substrate 1 and at the outside ofopposite ends of the circuit region 2.

On the other hand, a package substrate for supporting the sensor chip 10thereon is partially shown in the drawing, and generally designated byReference Numeral 14. This package substrate 14 includes a plurality ofbonding stitches (or pads) 3 formed thereon at both sides of thesubstrate 1 in the following manner: These bonding stitches 3 can bedivided into first and second arrays 20 and 22 which includesubstantially the same number of bonding stitches (six bonding stitchesin the shown embodiment) and which are located in parallel to alongitudinal direction of the substrate 1 so that the first array 20 ofbonding stitches 3-1, 3-2, 3-3, 3-4, 3-5 and 3-6 are arranged at oneside of the substrate, and the second array 22 of bonding stitches 3-11,3-12, 3-13, 3-14, 3-15 and 3-16 are arranged at the other side of thesubstrate. In addition, the bonding stitches 3 can be also divided intofirst and second groups 30 and 32 which include substantially the samenumber of bonding stitches (six bonding stitches in the shownembodiment) and which are separated from each other in the longitudinaldirection of the substrate so that the first group 30 of bondingstitches 3-1, 3-2, 3-3, 3-11, 3-12, and 3-13 are positioned in theproximity of one end zone 1B of the substrate, and the second group 32of bonding stitches 3-4, 3-5, 3-6 3-14, 3-15 and 3-16 are positioned inthe proximity of the other end zone 1C of the substrate.

Each one of the bonding pads 4 is connected to a corresponding one ofthe bonding stitches 3 by a boding wire 5. Specifically, the bondingpads "a₁ " to "a₆ " in the end zone 1B (at a left side of the circuitregion 2 in the drawing) are connected to the bonding stitches 3-1, 3-2,3-3, 3-11, 3-12, and 3-13 included in the first group 30 in such amanner that odd-numbered bonding pads "a₁ ", "a₃ " and "a₅ " areconnected to the bonding stitches 3-11, 3-12, and 3-13 in the secondarray 22, respectively, and even-numbered bonding pads "a₂ ", "a₄ " and"a₆ " are connected to the bonding stitches 3-1, 3-2 and 3-3 in thefirst array 20, respectively. The bonding pads "a₇ " to "a₁₂ " in theend zone 1C (at a right side of the circuit region 2 in the drawing) areconnected to the bonding stitches 3-4, 3-5, 3-6 3-14, 3-15 and 3-16included in the second group 32 in such a manner that odd-numberedbonding pads "a₇ ", "a₉ " and "a₁₁ " are connected to the bondingstitches 3-14, 3-15, and 3-16 in the second array 22, respectively, andeven-numbered bonding pads "a₈ ", "a₁₀ " and "a₁₂ " are connected to thebonding stitches 3-4, 3-5 and 3-6 in the first array 20, respectively.Thus, each bonding wire can connect each bonding pad to a correspondingbonding stitch with a short distance and without crossing anotherbonding wire.

As seen from the above, since the pair of bonding pad groups are locatedin opposite end zones of the elongated substrate 1 and at the outside oflongitudinal opposite ends of the circuit region 2, a distance D betweeneach side edge of the substrate 1 and a corresponding side edge of thecircuit region 2 can be made sufficiently smaller than a size of thebonding pads. In other words, it is possible to reduce the width of theelongated substrate 1 so as to approach the width of the circuit region.With this arrangement, the empty area at each side of the circuit region2 can be made to almost zero.

In addition, the bonding stitches 3 are divided into the first array 20of bonding stitches connected to the even-numbered bonding pads "a₂ ","a₄ ", "a₆ ", "a₈ ", "a₁₀ " and "a₁₂ ", and the second array 22 ofbonding stitches connected to the odd-numbered bonding pads "a₁ ", "a₃", "a₅ ", "a₇ ", "a₉ " and "a₁₁ ", and the first array 20 of bondingstitches are located on one side of the substrate 1 and the second array22 of bonding stitches are located on the other side of the substrate 1.With this arrangement, even if the pitch P₂ of the bonding stitches 3were made a double the pitch P₁ of the bonding pads 4, it is possible toconnect each bonding pad to a corresponding bonding stitch by a bondingwire without any trouble.

In ordinary cases, the width d₁ of the bonding pads 4 is on the order of100 μm, and the space d₂ between each pair of adjacent bonding pads 4can be narrowed to about 25 μm. Therefore, it is possible to arrange thebonding pads with the pitch P₁ of 125 μm. On the other hand, the widthS₁ of the bonding stitches 3 is on the order of 160 μm, and the space S₂between each pair of adjacent bonding stitches 3 needs at least about 90μm. Therefore, in order to arrange the bonding stitches 3, the pitch P₂of at least 250 μm is required. In the embodiment shown in FIG. 1, thepitch P₁ of the bonding pads can be reduced to the minimum pitch of 125μm while maintaining the pitch P₂ of the bonding stitches 3 at 250 μm.In other words, it becomes unnecessary to expand the pitch P₁ of thebonding pads in order to ensure the minimum pitch P₂ of the bondingstitches 3. Accordingly, it is very effective in shortening the lengthof the sensor chip.

Referring to FIG. 2, there is shown a modification of the embodimentshown in FIG. 1. In the modification, the bonding pads 4 included ineach of the boding pad groups are staggered to depict a single zigzagline in the extent of the width of the substrate 1. Each boding pad 4 isin a rectangular shape having each side inclined to the side edge of thesubstrate by 45°. With this modification, as seen from comparisonbetween FIGS. 1 and 2, the modification shown in FIG. 2 is veryeffective in reducing the empty area in the periphery of the bondingpads 4. Therefore, it is further effective in shortening the length ofthe sensor chip.

The invention has thus been shown and described with reference to thespecific embodiments. However, it should be noted that the presentinvention is in no way limited to the details of the illustratedstructures but changes and modifications may be made within the scope ofthe appended claims.

I claim:
 1. A linear image sensor comprising:a linear image sensor chipformed of an elongated semiconductor substrate and including a circuitregion having therein a number of photosensitive elements and located ina center zone of said substrate in a longitudinal direction of saidsubstrate, and a pair of bonding pad groups located in opposite endzones of said substrate and at the outside of longitudinal opposite endsof said circuit region, each of said bonding pad groups including aplurality of bonding pads formed on said substrate; a package forsupporting said substrate thereon, and including a plurality of bondingstitches formed on said package, said bonding stitches being dividedinto first and second arrays which include substantially the same numberof bonding stitches and which are located in parallel to a longitudinaldirection of said substrate so that said first array of bonding stitchesare arranged at one side of said substrate, and said second array ofbonding stitches are arranged at the other side of said substrate, saidbonding stitches being also divided into first and second groups whichinclude substantially the same number of bonding stitches and which areseparated from each other in the longitudinal direction of saidsubstrate so that said first group of bonding stitches are positioned inthe proximity of one of said end zones of said substrate, and saidsecond group of bonding stitches are positioned in the proximity of theother of said end zones of said substrate; and a number of bonding wireseach connecting one of said bonding pads to a corresponding one of saidbonding stitches without crossing another bonding wire.
 2. A linearimage sensor claimed in claim 1 wherein a distance between each sideedge of said substrate and a corresponding side edge of said circuitregion is smaller than a size of said bonding pads.
 3. A linear imagesensor claimed in claim 2 wherein in each of said bonding pad groups,said bonding pads are arranged in a single line, and even-numberedbonding pads of said bonding pads on said single line are respectivelyconnected to corresponding ones of said bonding stitches included insaid first array, and odd-numbered bonding pads of said bonding pads onsaid single line are respectively connected to corresponding ones ofsaid bonding stitches included in said second array.
 4. A linear imagesensor claimed in claim 3 wherein said bonding pads included in each ofsaid bonding pad groups are aligned in a single straight line.
 5. Alinear image sensor claimed in claim 3 wherein said bonding padsincluded in each of said bonding pad groups are staggered to depict asingle zigzag line.
 6. A linear image sensor claimed in claim 5 whereineach of said bonding pads is of a rectangular shape having each sideinclined to a side edge of said substrate by 45°.